The objective of this project is 1) to explore in rats the interrelationship between the functional and histological response of ocular tissue to infection and injury when vitamin A deficiency coexists at varying levels of severity, and 2) to seek evidence that correlates the findings in rats to human children subclinically and clinically deficient in vitamin A. More than 100,000 children are blinded annually or have impaired vision from vitamin A deficiency, and an undetermined additional number are likely to have their health compromised by a decreased resistence to infection. Little is understood about the sequence of compromised functions that occur with progressive vitamin A deficiency, particularly with respect to infections, and how these might relate to the occurrence of keratomalacia. This project will systematically determine in rats the effect of relative states of vitamin A deficiency on cell-mediated and humoral immune function of ocular tissue and relate this to the systemic resonse with and without infection. Histological changes in ocular tissue and major organs will be determined concurrenly as will changes in the ocular microflora. The effect of trauma in the form of infection (local or systemic) or ocular injury on the release of collagenase in the development of keratomalacia will be determined. A method for indirectly assessing depleted liver stores of vitamin A developed previously (relative dose response) will be tested in rats with lowered plasma levels of vitamin A due to infection and in children believed to be subclinically and clinically deficient.